This invention relates to instruments for detecting acceleration on moving objects, and more particularly to a capacitive accelerometer.
It is already well known in the prior art that a capacitive accelerometer consists of a pair of magnetic units and a flapper or pendulum of nonconductive material such as, for example, fused quartz coated with metal, the flapper being interposed between the magnetic units having permanent magnets so as to be displaceable relative thereto. In this capacitive accelerometer, each metal coated surface of the flapper is provided with a coil surrounding one of the permanent magnets. In the operation of the heretofore accelerometers, when acceleration is applied to the accelerator, the flapper will deflect and cause a change in capacitance with respect to each of the magnetic units. This change is modulated and amplified by an external circuit and is fed back to the coils as a direct current. This current gives rise to a force or torque on the flapper for restoring it to a null position. The current required to restore the flapper to the null position is a measure of the acceleration applied to the accelerometer.
Japanese Utility Model Publications No. 52-38218 and No. 52-38219 respectively disclose a capacitive accelerometer of the above type in which the flapper or pendulum is made of conductive material such as, for example, beryllium copper and one end of the flapper is clamped by a pair of ring-like holders.
When the flapper is made of nonconductive material such as fused quartz as mentioned above, it is necessary to coat the surface of the nonconductive flapper with conductive material. Accordingly, the flapper of each of the accelerometers shown in the above publications is made of beryllium copper for avoiding troublesome coating process. The accelerometer must be assembled precisely with great care, which makes it extremely expensive to manufacture. When the flapper is made of metal, the supporting portion of the flapper in contact with metallic holder different in material from the flapper is subjected to thermal stress due to the difference of thermal expansion between the flapper and the holder.
Further, a coil wound on a bobbin made of different material from one of the flapper must be mounted on both sides of the flapper, and the portion of the flapper attached to the bobbin will be subjected to thermal stress as mentioned above and also the flapper will be loaded by conductors for connecting the coils to the external circuit.
In addition to the above, the flapper must be hinged flexibly relative to the holder, and the hinged portion will be subjected to inner mechanical stress on working. This stress is often of disadvantage to performance of the accelerometer.